1. Field of the Invention
This invention relates to an engine valve train device for continuously controlling an opening duration or a lift of a valve.
2. Description of the Related Art
Conventionally, engine valve train devices for continuously controlling an opening duration and a lift of a valve have been in practical use. For example, there has been proposed such a valve train device in JP-A-Sho59-500002, in which, to open and close intake and exhaust valves by cam shafts via rocker arms, a swinging member for each valve is disposed and swung by the camshaft, an intermediate roller is interposed between a swing cam face of the swinging member and the rocker arm, and the valve opening duration and the valve lift can be continuously changed by displacing the intermediate roller.
Now, in such conventional valve train devices, the shorter the valve opening duration, the smaller the lever ratio of the rocker arm, and, in contrary, the longer the valve opening duration, the larger the lever ratio of the rocker arm. Due to the larger lever-ratio for a longer valve opening duration, a distal end of the rocker arm presses against the valve, and the intermediate roller presses against the intermediate portion of the rocker arm. As a result, it is difficult to secure rigidity of the entire valve opening/closing device. In particular, accuracy of control over the valve opening duration and the valve lift is apt to reduce during operation at high engine speeds. Further, due to a smaller lever-ratio for a shorter valve opening duration, it is difficult to secure the valve lift for a shorter valve opening duration, which is disadvantageous for reduction of pumping loss and improvement of combustibility. Thus, controllability of valve opening and closing timing is also apt to worsen.